The Solar System

The Solar System

  • It is the name given to the group of the Sun and it’s major planets, i.e., Mercury, Venus, Earth, mars, Jupiter, Saturn, Uranus, Neptune and their satellites, asteroids etc. They are kept in their position due to their respective gravities.        
  •  Planet is the name given to a heavenly body which revolves around the sun in elliptical orbit. A planet has no light of its own but reflects the light of the sun. Star is the name given to a fixed heavenly body which has its own light. The sun is a star and not a planet.
  • The life a star is spread over billions of years. It begins to form by compression of galactic gas and dust. Compression generates heat which in turn causes hydrogen to be converted into helium in nuclear fusion, thereby emitting large amount of heat and light.
  • Continued nuclear fusion over a period of time starts depletion of hydrogen and the helium core becomes increasingly heavy, resulting into swelling and reddening of outer regions. Such stars of gigantic dimensions are termed as Red Giants.
  • If the star is of sun’s size, it becomes a White Dwarf. Their central density can reach up to 10° grams per cubic cm.
  • If the star is bigger than the sun but not more than twice as big, it will turn into a Neutron Star or Pulsar. Their central density is 1014 grams per cubic cm. They are formed due to Novae or Super novae explosion.
  • Stars having mass greater than three times that of the sun, because of their greater gravitational power, have contracted so much that they have developed super density of about 1016 grams per cubic cm. It is so dense that nothing, not even light, can escape from its gravity and hence called ‘Black Hole’.
  • Brightest star outside our Solar System is Sirius, also called Dog Star.
  • Closest star of Solar System is Poxima Centauri (4.2 light years away). Then come Alpha Centrauri (4.3 light years away) and Barnard’s Star (5.9 light years away).

Distance from the earth*

149.8 million km

Absolute Visual Magitude



1384000 kilometre

Core Temperature

5770 K

Rotation as seen from the earth

25.38 days (at the equator)

33 days (near the poles)

30 days (at latitude 60°)

Chemical composition (by volume)

Hydrogen 81.76% Helium 18.17%, Oxygen 0.03%, Magnesium 0.02%, Nitrogen 0.01%, other Elements 0.01%


About 5 billion years

Expected lifetime of a normal star

About 10 billion years

Linear velocity (at equator

2 km per second